The spread of wireless systems that use microwave/millimeter wave band waves for wireless LANs, wireless sensor networks, and wireless transmission of high-quality audio-visual signals and the like has brought with it a demand for lower-priced wireless apparatuses. In particular, a feature of millimeter wave band communication is that the apparatus can be miniaturized, which is expected to lead to its widespread utilization for short-range communication in the home and office. On the other hand, the promotion of its use and its popularity are hindered by the problems of the high cost of developing and manufacturing the communication apparatuses due to the extremely high frequencies, and poor power efficiency.
A conventional, general microwave/millimeter wave communication apparatus comprises forming an RF transmission/reception circuit by connecting together the functional circuits with a transmission line, and using a power supply line to connect the transmission/reception circuit and the antenna. For example a structure in which an oscillator MMIC (Monolithic Microwave Integrated Circuit) chip, an amplifier MMIC chip, mixer MMIC chip and microstrip type patch antenna are connected by a microstrip line.
In such a communication apparatus formed by connecting individual circuits, there is a limit to the high-density integration of circuits. With millimeter wave bands in particular, loss due to the connecting portions between the functional circuits and loss due to the transmission line are major causes of circuit performance degradation. To counter such problems in a communication apparatus in which individual circuits are connected, there have been proposed active antenna technology that integrates the antenna and the RF circuit section, and a communication apparatus that aims at achieving simple structure, low cost, and low power consumption by utilizing radiating oscillator technology that integrates the amplifier element and electromagnetic wave radiation structures.
Examples include a communication apparatus that uses radiating oscillator technology in which a GUNN diode as the oscillating element is mounted inside a conductor patch, (see, for example, C. M. Montiel, L. Fan and K. Chang, “A Self-Mixing Active Antenna for Communication and Vehicle Identification Applications”, IEEE MTT-S Digest, pp. 333-336, 1996 (Non-patent Literature 1)), a communication apparatus in which a transistor is placed at the center of two half-round conductor patches capacitively coupled by a capacitor component, a bias chip resistor and Schottky barrier diode are also placed inside the same conductor patch, and the transistor is used as an oscillating element, and the Schottky barrier diode is used as a receiving wave down-conversion mixing element to form a radiating oscillator (see, for example, Robert A. Flynt, “Low Cost and Compact Active Integrated Antenna Transceiver for System Application”, MTT-10 vol. 44, October 1996 (Non-patent Literature 2)), a communication apparatus that uses active antenna technology having a structure in which a microstrip line transistor oscillation circuit and a receive wave amplifier circuit on a square conductor patch have the shortest connection on the same plane (see, for example, M. J. Cryan and P. S. Hall, “Integrated active antenna with simultaneous transmit-receive operation”, Electronics letters, February 1996 vol. 32, No. 4, pp. 286-287 (Non-patent Literature 3)), and a communication apparatus using active antenna technology having a structure in which a microstrip line transistor resonator circuit is connected to a rectangular conductor patch (see, for example, F. Carrez and J. Vindevoghel, “Integrated circuit array antenna for short-range communication systems”, Electronics letters, July 1998 vol. 34, No. 14, pp. 1370-1371 (Non-patent Literature 4)).
With the communication apparatus described in the above Non-patent Literature 1, frequency modulation is generated by superposing a high-frequency signal on the direct-current bias of a GUNN diode and emitting it to an apparatus formed in the same way, causing an injection-locking phenomenon and at the same time transmitting the frequency modulation component to another radiation type oscillator, whereby the high-frequency component is transmitted by the mixing operation of the GUNN diode itself. Via a bias-T circuit, the frequency modulation component is superposed on the direct-current bias or isolated. Also, in using the communication apparatus described in the above Non-patent Literature 2, two communication apparatuses that are the same are used in opposition, positioned with the radiation polarization planes at 90 degrees to each other, so that the oscillated radiation signals do not mutually affect each other. The communication apparatus described in the above Non-patent Literature 3 does not specifically disclose the receive RF signal down-conversion or demodulation operations. Also, the communication apparatus described in the above Non-patent Literature 4 is comprised so that, during the receive operation, it is operated as just a diode wave detector with no direct-current bias applied to the transistor drain, and during transmit operation, the transistor is oscillated and the modulation signal input to the gate for the frequency modulation operation.
However, although with the configuration described in Non-patent Literature 1, there is no power loss from the transmission line, the DC/RF conversion efficiency of the GUNN diode is extremely low compared to that of a transistor, so power consumption is increased and a high heat dissipation structure must be used, so stable operation cannot be expected. In addition, the direct-current bias current provided to the GUNN diode is extremely large compared to when a transistor is used, so to sufficiently superpose the modulation signal component on the direct-current bias requires heavy-current driver circuitry, bias-T with a large current capacity and so forth, driving up the cost. Therefore, a communication apparatus having a simple structure, low cost, and high power efficiency cannot be realized with the invention described in Non-patent Literature 1.
Also, the configuration described in Non-patent Literature 2 is complex, with a plurality of RF band parts being positioned within the conductor patch. Moreover, because the mixing by the Schottky barrier diode is a general down-conversion operation of the oscillation signal as a LO signal, it is necessary to include an oscillation frequency stabilization circuit and synchronization circuit to carry out good communication with frequency modulation and the like, thereby increasing the cost. Therefore, a communication apparatus having a simple structure, low cost, and high power efficiency cannot be realized with the invention described in Non-patent Literature 2.
Also, the circuit of the configuration described in Non-patent Literature 3 is complex, with an electromagnetic coupling that is difficult to avoid between the square conductor patch and the microstrip line, and because it sensitively effects on the radiation output, radiation pattern and oscillation frequency characteristics, it is not practicable to use it as a stable communication apparatus. Further, to obtain an IF signal or baseband signal, it is necessary to equip the output unit of the receive wave amplifier circuit with a mixer and wave detector, making it costly. Therefore, a communication apparatus having a simple structure, low cost, and high power efficiency cannot be realized with the invention described in Non-patent Literature 3.
The circuit of the configuration described in Non-patent Literature 4 is also complex, with an electromagnetic coupling that is difficult to avoid between the square conductor patch and the microstrip line, and because it sensitively effects on the radiation output, radiation pattern and oscillation frequency characteristics, it is not practicable to use it as a stable communication apparatus. Although the single transistor has transmission/reception functions and modulation/demodulation functions, the baseband circuit has a complex configuration because the receive signal is amplitude modulated and the transmit signal is frequency modulated. Also, communication cannot be effected even if two of the same apparatuses are set in opposition, making it necessary to separately prepare a different type of apparatus as the other party to the communication. Therefore, a communication apparatus having a simple structure, low cost, and high power efficiency cannot be realized with the invention described in Non-patent Literature 4.
Thus, an object of the present invention is to solve the problems of complex structure, high cost and high power consumption that have hindered the dissemination of microwave/millimeter wave communication, by providing a microwave/millimeter wave communication apparatus that has a simple structure, low cost, and low power consumption.